This invention pertains to the measurement of the volume of liquid in a fuel tank, and in particular to the measurement of volume of liquid in an underground fuel tank using ultrasound.
Fuel such as gasoline is typically stored in underground storage tanks where the volume of fuel cannot be visually or directly determined. In the past, one commonly used method to measure the volume of fuel in the tanks was by use of a calibrated measuring rod which was manually inserted into a tank standpipe which was also used to fill the tank. In recent years improvements have been made to the art of measuring the volume of liquid which have eliminated the use of manual methods. These improvements have produced apparatus which is highly accurate in the measuring of liquid volume. In many instances, these improvements have been necessitated by governmental regulations which mandate that leaks from underground storage tanks be detected.
The cost of cleaning up environmental leaks is high. It is much more economic to detect leaks early so that necessary repairs and environmental cleanup can be done at the lowest possible cost.
Various systems have been developed which utilize a probe which is suspended or supported in the underground fuel tank. The probe is connected to a control console which is physically remote from the probe. The type of probe utilized is dependent on the type of measuring technique utilized. In one type of system, an ultrasonic transducer is suspended at the bottom end of a long probe.
The ultrasonic transducer is operated by periodically applying a pulse to the transducer. The transducer is excited by the pulse to produce an ultrasonic signal which propagates generally vertically in the tank. Ultrasonic echoes produced by the surface of the liquid and/or reflectors are indicative of the liquid depth in the tank. The echo delay time can therefore be utilized to calculate the volume of the liquid in the tank.
One problem arises in the use of ultrasonic probes which are physically located at great distances from the control console. For example, in some applications, it may be required to run up to a 500 foot cable between the transducer and the drive electronics located at the control console. Long cable runs severely attenuate the drive signals. Also, the return echo signals also become severely attenuated with long cable runs.
In one prior arrangement, a transformer is positioned near the transducer to provide for impedance matching to the transducer. However this arrangement is not entirely satisfactory.
It is therefore desirable to provide a means for operating ultrasonic transducers of the type utilized in ultrasonic probes used to measure the volume of fuel in an underground tank from a control console located up to a long distances from the probes.